1. Field of the Invention
The invention pertains to a self-pumping hydropneumatic spring strut with internal level control, especially for motor vehicles, with an oil-filled working cylinder under the pressure of at least one gas cushion located in a high-pressure chamber and acting as a spring, the working cylinder being divided into two working spaces by a working piston carried by a hollow piston rod. A piston pump is driven by the movements of the spring and conveys oil from a low-pressure chamber into the working space connected to the high-pressure chamber, the pump cylinder of the piston pump being formed by the hollow piston rod, into which a hollow pump rod, which is attached to the working cylinder and carries at its forward end a suction valve, travels, the bore of the hollow pump rod being connected to the low-pressure chamber. A down-regulating opening can be closed as a function of the position of the working piston in the working cylinder, and connects the working space connected to the high-pressure chamber to a down-regulating channel, which is itself equipped with a throttle and/or check valve and which opens out into the low-pressure chamber. Fluid flows through the check valve and/or the throttle in the suction direction, and that the pump cylinder is connected to the high-pressure-side working space by an outlet valve.
2. Description of the Related Art
Self-pumping hydropneumatic spring struts with internal level control are already known (e.g., U.S. Pat. No. 6,234,462, DE 196 48 859 C2), in which the working cylinder is divided by a working piston carried by a hollow piston rod into two working spaces, and in which a piston pump, which is driven by the movements of the spring and conveys oil from a low-pressure chamber into the working space connected to the high-pressure chamber, is provided. The piston pump consists of a pump cylinder, which is formed by the hollow piston rod, into the forward end of which the hollow pump rod, which carries a suction valve, travels. In this state of the art, a total of three spring-loaded check valves is provided, i.e., an inlet valve, an outlet valve, and a discharge valve. The inlet and outlet valves are necessary for the pumping work of the piston pump, and the discharge valve is necessary for the throttled discharge of the damping medium when the load being imposed by the vehicle body is removed. The disadvantage is that each of these valves has a different design, which means that the associated multiplicity of parts requires a not inconsiderable amount of work with respect to logistics and assembly. In particular, spring-loaded plate valves are so large that they cannot be installed in a relatively small-diameter pump rod.